This problem has persisted since the start of Season 10 (or TU16, and TU16.1). I have recorded a video showing the problem:
">When trying to mark all my unwanted gear as junk so I can one-shot scrap them all for materials, or donate them to Expertise, the function fails to work despite repeated attempts, thus forcing me to mark them one by one as junk. I am currently running the game on PC.
Developers, if there is any other information you need, please let me know. I have also made a tweet about this problem on Twitter. Thank you!